Method for regulating knocking

ABSTRACT

A method for controlling knocking in multi-cylinder internal combustion engines in KC emergency operation and at activated guide-cylinder function are provided by which a torque loss is able to be avoided at low application expenditure and the functionality desired by the guide-cylinder function is maintained even in KC emergency operation. In KC emergency operation and when the guide-cylinder function is activated, cylinder pairs are formed from the cylinders operating in each case at a  360 ° offset. Each twin pair having at least one cylinder to be guided is assigned at least one of the available guide cylinders, so that the ignition timing retard of the cylinder pair to be guided is based on the ignition timing retard of the associated guide cylinder. Only when the number of available guide cylinders is insufficient will a safety retard timing be triggered, in which an ignition angle is adjusted which has been predefined for all cylinders.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for controllingknocking in multi-cylinder internal combustion engines having 2 ncylinders, at least one of the cylinders being able to function as aguide cylinder for a cylinder designated to be the guided cylinder uponactivation of a guide-cylinder function, having a cylinder counter, atleast one knock sensor and an evaluation unit for evaluating theknock-sensor signals from the individual cylinders.

[0002] The evaluation of the knock-sensor signals is usually performedwith the aid of individual knock-detection characteristics for eachcylinder.

BACKGROUND INFORMATION

[0003] Knocking is understood as an uncontrolled form of combustion,which may lead to engine damage. For this reason, the ignition angle isnormally always selected with a safety distance to the knock limit. Onthe other hand, it is known that an internal combustion engine should beoperated as close as possible to the knock limit in order to achieveoptimum torque. Thus, keeping the ignition angle at a safety distance tothe knock limit results an increased fuel consumption. The knock limitdepends on a variety of factors during the operation of an internalcombustion engine, such as fuel quality, engine state and environmentalconditions. In order to be able to select the safety distance as smallas possible, that is, to be able to bring the ignition angle as close aspossible to the instantaneous knock limit, the respective instantaneousknock limit must first be determined in each case. It is standardpractice to use knock sensors for this purpose, such as structure-bornenoise sensors or combustion chamber pressure-sensors.

[0004] The knock-sensor signal is individually evaluated for eachcylinder. Assigning the instantaneous knock-sensor signal to aparticular cylinder, which is required for this purpose, is performedwith the aid of the cylinder counter within the framework of a phasedetection in which the states of the individual cylinders duringoperation of the internal combustion engines are detected. Under certainconditions, if the phase detector fails, it no longer possible todetermine whether the knock-sensor signal which is to be assigned to thecylinder corresponding to the cylinder-counter reading is beingevaluated or that of the cylinder running at a 360 degree offset. Thiscase is called knock-control (KC) emergency operation.

[0005] In practice, given KC emergency operation, the knock-detectionthreshold having the most sensitive setting of all cylinders is selectedand used as the basis of the ignition-timing control for all cylinders.The selection of the corresponding knock-detection characteristic mustthen be checked whenever the knock-detection threshold has been changed,so that undetected knocks and, thus, engine damage may be avoided.

[0006] Independently of KC emergency operation, it may occur that,starting with a specific rotational speed, a reliable knock detection isno longer possible for individual cylinders. In this case, the affectedcylinder is designated as a cylinder to be guided, and the so-calledguide-cylinder function is activated. In this way, one or even aplurality of guide cylinders is/are assigned to the cylinder to beguided. The cylinder to be guided is then operated at the ignitiontiming retard of the guide cylinder(s) and, if appropriate, has anadditional offset applied. If it is not possible to assign a guidecylinder to an affected cylinder, the latest ignition angle of theremaining cylinders is used for this cylinder. In this case, theignition angle may have an additional offset applied as well.

[0007] In practice, it may occur that the guide-cylinder function isactivated in KC emergency operation. In this case, the so-calledsafety-ignition retard is triggered in which an ignition angle is setwhich has been predefined for all cylinders. The resultant setting ofthe ignition angles to retard causes a high loss in torque.

SUMMARY OF THE INVENTION

[0008] The present invention provides a method for knock control in KCemergency operation and activated guide-cylinder function which make itpossible to avoid torque loss and to maintain the functionality desiredby the guide-cylinder function even in KC emergency operation, whilekeeping the application cost low.

[0009] According to the present invention, this is achieved in that inKC-emergency operation and at activated guide-cylinder function

[0010] cylinder pairs are formed from those cylinders running in eachinstance at an offset of 360 degrees;

[0011] each twin pair having at least one cylinder to be guided beingassigned at least one of the available guide cylinders, so that theignition timing retard of the associated guide cylinder forms the basisof the ignition timing retard of the cylinder pair to be guided;

[0012] and a safety retard timing in which an ignition angle is set thathas been predefined for all cylinders is triggered only when nosufficient number of guide cylinders is available.

[0013] According to the present invention, a knock control or anignition timing control in KC emergency operation and a knock control orignition-timing control with guide-cylinder function are interlinked insuch a way that the ignition timing control is performed as a functionof the state of the respective cylinder. This is because the knockcontrol according to the present invention takes into account bothwhether a cylinder is affected by the unavailability of phase detectionand also whether a reliable knock detection is still possible for acylinder at the given rotational speed. For this purpose, according tothe present invention, the cylinders of the internal combustion enginesare combined into cylinder pairs. The ignition angles of the cylindersof a cylinder pair to be guided are uniformly controlled in KC emergencyoperation. Compared to a safety timing retard for all cylinders, theforming of cylinder pairs according to the present invention and thepair-wise control according to the present invention allows earlierignition angles for at least some of the cylinders of the internalcombustion engine, so that a torque gain is able to be achieved.

[0014] If a plurality of guide cylinders is assigned to the cylinderpair to be guided, the greatest torque gain may be achieved byascertaining in each case the minimum of the ignition timing retards ofall guide cylinders of the cylinder pair to be guided and this minimumof the ignition timing retards forming the basis for the ignition timingretard of the cylinder pair to be guided.

[0015] For reasons of application safety, it is advantageous if thecylinder pair to be guided is operated at the ignition timing retard ofthe guide cylinder or the minimum of the ignition timing retards of allthe assigned guide cylinders plus an applicable offset.

BRIEF DESCRIPTION OF THE DRAWING

[0016] The FIGURE shows a switching logic for realizing the methodaccording to the present invention for a four-cylinder engine.

DETAILED DESCRIPTION

[0017] Reference numerals 11 and 12 denote the igniting-timing retardsignals of two cylinders of a four-cylinder engine which operate at a360° offset and are combined to form a first cylinder pair in the eventof KC emergency operation. The ignition timing retard signals from theother two cylinders of the four-cylinder engine are denoted by referencenumerals 21 and 22. These other two cylinders form a second cylinderpair in KC emergency operation.

[0018] The case shown here is not limited to KC emergency operationonly. In addition, starting with a certain rotational speed, a reliableknock detection is also no longer possible for at least one of the twocylinders of the first cylinder pair. For this reason, the firstcylinder pair is designated to be the one to be guided. In the case athand, upon activated guide-cylinder function, both cylinders of thesecond cylinder pair are assigned to the first cylinder pair as guidecylinders.

[0019] To determine the respective ignition timing retard for the firstcylinder pair, the minimum of the ignition timing retard signals 21 and22 of the second cylinder pair is determined in each case with the aidof a switching element 3. A safety offset 5 is added to this minimum bya summation element 4. The result is supplied to a switch 1 at whichignition timing retard signal 11 of a cylinder of the first cylinderpair is present as well. Furthermore, the result is supplied to a switch2 at which ignition timing retard signal 12 of the other cylinder of thefirst cylinder pair is present as well.

[0020] If, on the one hand, the condition for KC emergency operation 7and, on the other hand, the condition for guide-cylinder function 8 aswell are present at the respective inputs of a logical AND-linkingelement 6, switches 1 and 2 are activated, so that, as the ignitiontiming retard signals 110 and 120 of the cylinders of the cylinder pairto be guided, the minimum of the ignition timing retard signals 21 and22 of the second cylinder pair is used plus the added-on safety offset5. This minimum selection has the effect that the latest ignition angleis used for the guided cylinders.

What is claimed is:
 1. A method for controlling knocking inmulti-cylinder internal combustion engines having 2 n cylinders, atleast one of the cylinders, upon activation of a guide-cylinderfunction, being able to function as a guide cylinder for a cylinderdeclared to be guided; having a cylinder counter; at least one knocksensor; and an analyzing device for analyzing the knock-sensor signalsof the individual cylinders; wherein, in knock-control (KC) emergencyoperation, i.e., when phase detection fails, i.e., the analyzing deviceis unable to determine whether the knock-sensor signal is to be assignedto the cylinder corresponding to the cylinder counter reading or to thecylinder operating at a 360° offset, and when the guide-cylinderfunction is activated, cylinder pairs are formed from the cylindersrunning in each instance at an offset of 360 degrees; each twin pairhaving at least one cylinder to be guided being assigned at least one ofthe available guide cylinders, so that the ignition timing retard of thecylinder pair to be guided is based on the ignition timing retard of theassociated guide cylinder; and a safety retard timing, in which anignition angle is set which has been predefined for all cylinders, istriggered only in those cases where the number of available guidecylinders is insufficient.
 2. The method as recited in claim 1, aplurality of guide cylinders being assigned to the cylinder pair to beguided, wherein, in each instance, the minimum of the ignition timingretards of all guide cylinders of the cylinder pair to be guided isdetermined and the ignition timing retard of the cylinder pair to beguided is based on this minimum of the ignition timing retards.
 3. Themethod as recited in one of claims 1 or 2, wherein the cylinder pair tobe guided is operated at the ignition timing retard of the guidecylinder or the minimum of the ignition timing retards of all associatedguide cylinders plus an applicable offset.